Field of the Invention
The invention relates to a magnetoresistive semiconductor element that can be used, in particular, in read heads for reading out information stored in magnetic storage media. The invention also relates to a storage element, a field-effect transistor, a bipolar transistor, and a magnetic sensor, which include the magnetoresistive semiconductor element.
Magnetoelectronics and the spin-polarized transport of charge carriers have experienced rapid development in the last decade. This development was triggered primarily by the discovery of the so-called giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR). These two effects made it possible for the first time to convert a magnetic field, or an item of magnetization information, directly into a change in resistance. Both effects are based on the transport of spin-polarized electrons between two ferromagnetic contacts. The relative magnetization of the two contacts is crucial for the resistance of the overall component. In this case, GMR is utilized in purely metallic structures and TMR is utilized in structures with an oxide-type tunneling barrier between two ferromagnetic metal layers. At present, TMR structures are used for electronically readable magnetic memories MRAMS (magnetic random access memories), while GMR is commercially utilized primarily in magnetic field sensor technology and in hard disk read heads.
In the case of GMR, in a purely metallic component with two ferromagnetic contacts between which a layer of a nonmagnetic metallic conductor is arranged, the change in resistance between the parallel and the antiparallel magnetization is measured. With the application of an external field and hence a parallel orientation of the magnetizations in adjacent ferromagnetic layers, the resistance of the component decreases. On account of the metallic conductivity, the impedance of such an element is difficult to match to semiconductor circuits, which makes it more difficult to integrate GMR structures into such circuits.
In 1999, R. Fiederling, M. Keim, G. Reuscher, W. Ossau, G. Schmidt, A. Waag and L. W. Molenkamp (Nature 402, 787-790 (1999)) were able to demonstrate the injection of spin-polarized electrons into a nonmagnetic semiconductor by measuring the circular polarization of the light generated by a light-emitting diode. The polarization of the electron spins was achieved by injecting the electrons into a GaAs semiconductor via a Be0.07Mn0.03Zn0.9Se semiconductor contact. Circularly polarized light was generated by recombination with unpolarized holes injected from the opposite side of the layer of the GaAs semiconductor.